The broad goal of the proposal is to understand the functional organization of the early thalamocortical stages of processing in the auditory system. This involves a better functional understanding of the various pathways connecting the inferior colliculus (1C), medial geniculate body (MGB), and first and second auditory cortices (Al and All). We will use an in vitro slice preparation of the mouse brain in which different slice configurations will have the 1C to MGB, MGB to AI/AII, Al to MGB, and Al to All pathways intact. We will use uncaging of glutamate by photostimulation or minimal electrical stimulation to test the function of each of the pathways. In particular, we shall attempt to identify each pathway as a driver (i.e., main conveyer of information) or modulator, and by identifying the drivers, we hope to construct a functional hierarchy of information flow. This will allow us to test the hypothesis that a main route of information flow in the system is from the central 1C (ICc) to the ventral portion of MGB (MGBv) to Al to the dorsal MGB (MGBd, which we suggest is a higher order thalamic relay) to All. This is contrasted to conventional views: one is of parallel paths of ICc to MGBv to Al and shell region of 1C (ICs) to MGBd to All;another is a path from ICc to MGBv to Al to All. These hypotheses of functional organization are not mutually exclusive, and combinations may exist. Nonetheless, we must obtain a better understanding of how auditory information is routed through the first few stages of cortical processing before we can begin to understand how pathology in these pathways can lead to problems in hearing. That is, cognitive auditory functions, such as lexical-semantic processing, phonological information extraction, selective attention and object recognition are almost certainly subserved by auditory cortical networks, and it is these networks that we must better understand.